I’m surprised how many iOS and OS X devs don’t know about this. Git
Immersion is a great walk through of git, the wunderkind distributed
version control system that Apple has adopted in Xcode. Hats off to Edge
Case, a Ruby shop in Columbus, OH, for putting this thing together.

It’s slick and teaches you to think in git and not just rattle off commands
as if they were magical incantations learned at Hogwarts1. Yeah, yeah,
Xcode has a nice pretty interface to the git underpinnings. You need to
know git at the shell level. It’s the future, baby!